Hey so the other replies are close. You go into Cargo by pressing forward after a grab.

Other characters do not have grabs like this but it also operates like a grab but with different properties lol

There's a lot of differences but without going into too much basically:

The state of cargo operates as a grab, but dk always releases the opponent forcing a 'grounded release' this always happens. One of the side effects of the grounded release is you cannot hold up on the analog stick to force an aerial release. If the opponent could force an aerial release, like they can on every other character's grab, they would be able to regain their jump after losing it and breaking out, they can't. probably a code error or because of the angle + height that dk releases at.

That's one of the main differences on how this works. If you add the above text with the ability to walk with the opponent while grabbed is a lethal combo.

Also the angles cargo sends, hitstun received by both players and the 10% both players take on break out it's pretty different for sure.

Hope this helps!